During the paving run of a road paver, the layer thickness of the newly laid road pavement should be measured continually and, if possible, in real time. The calculation of the layer thickness and its visualization for an operator should particularly ensure that the road paver guarantees production of a minimum or a maximum layer thickness. This is important because the road laying contractor is bound to provide layer thicknesses agreed to by contract. It should likewise be achieved that the newly laid road pavement can be exposed to different weather conditions without thereby becoming damaged.
Different systems are known in practice for measuring the layer thickness of a newly incorporated road pavement. For example, devices are used that determine the layer thickness by means of ultrasound or radar. The technical disadvantage of such devices is that reflective bodies must be used for an exact layer thickness measurement in order to make it possible to locate the newly laid road pavement unambiguously.
According to another method for measuring the layer thickness of the road pavement, measurement bodies are inserted into the new road pavement until they reach the plane lying underneath. Disadvantageous here is that due to the insertion of the measurement bodies into the new road pavement, damage, such as, for example, unevenness, can remain.
Also known are systems that can, on the basis of a height measurement with respect to the subgrade and on the basis of an inclination measurement of the screed, calculate the thickness of layer that has been laid at a back edge of the screed. In the case of such systems, conventional distance sensors such as, for example, ultrasound or laser sensors, are used for the height measurement. For the inclination measurement of the screed, such systems are equipped with an inclination sensor that is mounted on the screed assemblage. Although it is possible to achieve good measurement results with these systems on some subgrades, layer thickness measurement systems that use an inclination sensor to determine the layer thickness tend, particularly on uneven ground, to deliver poor measurement results. It is also disadvantageous that an inclination sensor used for calculating the layer thickness is extremely sensitive to accelerations or abrupt changes in the inclination of the road paver or the screed, which leads to poor measurement results.
For example, DE 100 25 462 A1 describes a system for determining the layer thickness of a newly laid road pavement by using an inclination sensor. Disclosed therein is a device for determining the layer thickness on the basis of a predetermined distance between the position of a height sensor and the screed back edge, the registered height above the subgrade and a determined tow arm-screed assemblage inclination, which is registered by means of an inclination sensor. As was already indicated, in the case of such a solution the measurement result for the layer thickness greatly depends on the inclination sensor, which can already be irritated by small vibrations or accelerations. Even small errors of the inclination sensor are enough to cause large errors in the calculation of the layer thickness.
DE 100 25 474 A1 describes a device for determining the layer thickness of a laid material to be applied to a subgrade by a road paver, whereby the road paver has a tractor, at least one tow arm mounted rotatably on the tractor in a manner that allows the height to be adjusted, a floating screed rigidly attached to the at least one tow arm that, with the tow arm, forms a tow arm-screed assemblage and an undercarriage lying with its bottom side on the base. The device furthermore comprises a distance sensor attached in a stationary manner to the tractor for measuring a relative distance between a reference position of the tractor and a reference position of the tow arm-screed assemblage, whereby the reference position of the tractor has a predetermined positional relationship to the bottom side of the undercarriage, and the reference position of the tow arm-screed assemblage has a predetermined positional relationship to a lower back edge of the screed.
DE 198 51 153 C1 relates to a method for measuring a driving surface, in which the driving surface profile is registered metrologically. Understood as a driving surface hereby is, in particular, a traffic area, e.g., a street or a highway, that is set up with a number of coats or layers in the framework of highway construction or repair work. The invention furthermore relates to a system for carrying out the method with a mobile testing device.
EP 0 510 215 B1 describes a device for regulating a driving surface cover thickness. The device comprises height sensors and inclination sensors, all of which are arranged on a screed assemblage in such a way that they follow a movement of the screed.
U.S. Pat. No. 7,172,363 B2 refers to a paving machine. The paving machine can have a power source, a traction system, a hopper that is configured to hold paving material, and one or more conveyors that are configured to transfer the paving material from the hopper. The paving machine can also have a plate or a screed board that is configured to lay out a mat of the paving material. The paving machine furthermore comprises at least one front sensor that is mounted on a front part of the paving machine and configured in order to measure the height from a surface to the front sensor, and at least one rear sensor that is mounted on the paving machine and configured in order to measure the height from a surface of the mat to the rear sensor. The paving machine also comprises a controller that is configured to determine a thickness of the mat by determining a difference between one or more front height measurements that have been recorded by at least one front sensor, and one or more rear height measurements that have been recorded by the at least one rear sensor. The sensors are mounted on a support that is permanently connected to the screed.
In light of the obvious technical problems and disadvantages of the state of the art, the object of the present invention is therefore to provide a road paver having a measuring device for determining the layer thickness of a newly incorporated road pavement, whereby the measuring device is not sensitive to accelerations or changes in the inclination of the road paver, and consequently in this way allows an improved measurement result of the layer thickness.
This object is solved with the present invention as described below.